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FAQ: Engineered Plastic Piston Rings

Tech Talks by igus helping solve design engineering problems with motion plastics

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What are common applications for piston rings? Piston rings are precision split rings that fit around the circumference of a piston head, between the head and the inner cylinder wall. These rings are found in a variety of applications that use pistons such as liing elements and control valves and fittings. The hydraulics and pneumatics, transportation, food and beverage, and medical industries, among others, all use piston rings in one or more ways. What kinds of piston rings are available? Different kinds of piston rings are available for different applications. The first piston rings—still commonly found in combustion engines—are split metal rings that snap around the piston head. In other applications strips or stamped tapes of polytetrafluoroethylene (PTFE) polymer are chosen for their malleability and low-friction properties. These tapes may or may not be tailored to the specific application, but can conform to piston heads that don't have a constant diameter. Engineered plastic rings have the rigidity, temperature resistance, and durability that lets them compete with metal rings while also maintaining the non-reactive, corrosion-resistant, low-friction qualities of PTFE strips. These rings are oen wider than metal rings and feature an angled split that allows them to snap into place. the rings uniform mechanical and physical properties across their width and throughout their thickness. The even distribution of reinforcing fibers improves the piston rings' wear characteristics while guaranteeing even wear over their lifetime. Each type of engineered plastic formulation is specifically designed to perform in a given application environment. Different base polymers can give the piston rings excellent high- or low-temperature performance, low moisture absorption, chemical resistance, or strength among other properties. The inclusion of solid lubricant within the plastic removes the need for an external lubricant that must be periodically renewed. In comparison, metal rings require regular reapplication of oil or grease or use a polymer lubricant layer that wears away over time—both of which can be problematic in food and beverage and medical applications. Will engineered plastic rings work in my application environment? Engineered plastic piston rings use tailored polymer, lubricant, and reinforcement blends to meet the needs of a wide variety of application environments. For example, piston rings made from igus's iglide T500 materials can withstand temperatures from −148°F to 482°F. Plastic piston rings are not subject to the corrosion that can damage their metal counterparts. Most of the engineered plastics that go into these rings are unaffected or minimally affected by hydrocarbons, greases, fuels, and mild acids and alkalines. Rings made from iglide T500 are not affected by most chemicals except sulfuric and nitric acids in concentrations above 65%. For very moist or submerged environments, engineers choose engineered plastics with lower levels of moisture absorption or take swelling into account in their designs. Two examples of such materials are iglide H370, which gains less than 0.1% by weight in standard atmosphere and has a saturation limit in water that is also below 0.1%, and iglide J with a 0.3% moisture gain and 1.3% saturation limit. Food and beverage and pharmaceutical applications may need to choose piston rings that are FDA-compliant if they may come into contact with the product. Engineers choose materials like iglide A180, A350, and A500 for such applications. Engineered Plastic Piston Rings FAQs What are engineered plastic piston rings made of? Piston rings are made from homogeneous mixes of base polymer, reinforcing fibers, and solid lubricant. Homogeneous blending gives

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